It is presently common practice, when a section of sewer pipes perhaps newly laid, have to be tested to ensure these will withstand selected hydraulic pressures, that a sealing device be inserted the access for insertion being by way of a pipe joining in a T-section to the main sewer pipe or drain pipe such as a vertical riser.
A most common device presently used for effecting such closure for testing purposes is an inflatable balloon like member which is inserted in an uninflated condition through a vertical riser, and by pushing the uninflated member into the transverse pipe perhaps by using a rod and then inflating the balloon like member by means of a flexible conduit extending from the balloon like member to a surface, a sealing effect is obtained.
A first problem occurs in that if the walls of the pipe to be sealed are smooth, it is very often difficult to achieve sufficient inflation pressure without damage to the inflation member to ensure that the member will retain its position against the substantial hydraulic head that can arise under testing conditions.
If excessive pressure is required, the inflatable member can be damaged.
A second problem involves the difficulty of releasing the sealing pressure when the testing of the pipes has been completed.
It will be recalled that there is a substantial water head which is being held by the inflated member and as the inflation is reduced, this pressure will cause the sealing member upon a partial inflation to be pushed along the direction of the release of pressure.
In practice such release can result in the inflatable member being substantially wrenched along the pipe which can cause potential damage to the means such as the hollow conduit secured to the inflatable member and suddenly this can be subjected to substantial tension holding the inflatable member from being swept down the further length of the sewage pipe.
Furthermore many of the sewage pipes have some sharply projecting portions and these can result in the inflatable member tearing as it is swept past such sharp projections.
Where the vertical riser is a very short distance from a surface, a hand held sealing device has been used in which co-reacting plates expand a resilient sealing ring.
Such a device must be maneouvred by hand down the vertical portion of the pipe and then around the lower bend and then along the inner lower tube in which position a support arm extending along the axial direction of the sewage tube to be sealed is then held and suitable means provided whereby to effect an outward expansion of the resilient sealing ring.
Such an arrangement, while avoiding some of the problems of the inflatable member, still subjects the user to substantial difficulties when releasing sealing engagement when a head of water is behind the seal and such devices tend to be very quickly swept along the pipe so that the operator must exert substantial pressure by hand to stop such sealing device being swept along the pipe. Such devices are difficult to use, may result in injury to the user or may result in the apparatus being swept along the pipe which could result in an intolerable blockage at an inaccessible place further along the pipe.
Such then is the presently known art.